Thank you for this forum and thanks to Ernesto, Ruben, & Evan for their comments and questions. I will try to answer questions raised by them with respect to the "pH" article I published in the March/April 2014 issue of Concrete Repair Bulletin of ICRI.

1. The article shows a photograph identifying pH of concrete as 6. That is a wrong pH of concrete measured using present ASTM F 710 method.

2. Evan mentioned that typically shot blasting is not used for floor preparation. He mentioned to me that the concrete surface is cleaned by grinding the surface using sand pads. The test method I proposed in the above paper uses 50 grit sand paper to mimic exactly the sand pad type grinding.

3. I have seen shot blasting used prior to many flooring installations in CA. However, it does not matter if shot blasting is used or sand pad grinding is used. Both the sand pads or shot blasting do the same thing. It exposes freshly ground concrete surface along with cement/cementitious dust. When this cement/cementitious dust mixes with the water from the water based flooring adhesive or subsequent accumulation of water under a non-breathable vinyl flooring, then it creates a high pH solution at the interface of concrete to adhesive. If the adhesive cannot tolerate high pH condition, then it is susceptible to adhesive failure.

4. Yes, sometimes grinding hard steel troweled surface is difficult and may need power tool to grind the surface just like the sand pad grinding mentioned by Evan. That is why I proposed a 50 grit sand paper and not a 100 grit lighter sand paper. I have no problem using power tool to grind the surface to collect the dust for testing as long as we do not grind the concrete surface too deep. Hand grinding using a 50 grit sand paper has much better control in the grinding process.

5. If the concrete surface is carbonated, so be it. We will measure a lower pH. The idea is to measure the "True" pH of concrete surface and not a false pH as it is often measured and reported using ASTM F 710.

If you wish you can contact me directly with any technical question at ashokkakade@concretescience.com or at (510) 581-2342 extn. 107. Thanks.